PROJECT SUMMARY By age 50, almost one in three women, treated with chest radiation for a childhood cancer, will be diagnosed with breast cancer. Early detection of breast cancer is strongly associated with survival, and surveillance with annual breast MRI and mammography is recommended, starting at age 25. Unfortunately, the vast majority of these women are not adherent to the recommended surveillance. Magnifying this problem, most childhood cancer survivors are no longer followed at a cancer center, are unaware of their risks, and are being followed by primary care providers (PCPs) who are not informed about the recommended follow-up care. Based upon our prior findings in EMPOWER-I, we now propose EMPOWER-II, a 3-arm randomized controlled trial that extends the core component of the EMPOWER-I intervention (mailed educational materials) to evaluate the utility of patient activation with and without added PCP activation to increase breast cancer surveillance. We propose to randomize 291 women, who are at least 25 years of age, with a history of chest radiation for a childhood cancer, without a history of breast cancer, and without both a breast MRI and mammogram in the previous two years. The primary outcome is obtaining a breast MRI and mammogram during the 12-month study period. We will determine the comparative effectiveness of (1) a smartphone-based patient activation intervention and (2) patient activation plus PCP activation, compared to control. Secondary aims include exploring moderating and mediating factors that predict surveillance completion, timing of the obtained surveillance, and estimating the intervention replication costs and costs resulting from the intervention. The proposed EMPOWER-II study brings together a research team with the necessary expertise and experience in both survivorship research, smart-phone delivered interventions, and the unique resource of the 31-insitution Childhood Cancer Survivors Study (CCSS). Notably, the CCSS represents the single largest cohort of women in the target population and the infrastructure to conduct the proposed study. Results from this intervention will have important implications for all high-risk women treated with chest radiation at a young age.